1. Field of the Invention
The invention relates to a device for generating light pulses. The device comprises a seed laser source and an optical power amplifier which amplifies the light pulses generated by the seed laser source.
2. Description of the Related Art
Many applications require a tunable visible ultrafast source of light pulses. Fiber technology enables efficient maintenance free systems that generate femtosecond pulses (i.e. light pulses with a pulse duration between 1 fs and 1 ps) with nanojoule energies in the near infrared at a wavelength of 1.56 μm. Such a system can be used as a seed laser source for generating light pulses in a device of the type mentioned above.
The radiation of the seed laser source can be converted into wavelength-tunable radiation in the infrared spectral region using third-order non-linear processes in highly non-linear fibers (HNLF). The tunabilty of the near infrared radiation is achieved by varying the duration of the pulses incident onto the HNLF in a targeted manner. This radiation can be further converted, for example by means of second harmonic generation, to wavelength-tunable radiation in the visible spectral region.
For example from U.S. Pat. No. 7,202,993 B2 a system for the generation of wavelength-tunable light pulses is known. The known system comprises a femtosecond fiber laser as a seed laser source. The light pulses generated by means of the seed laser source are pre-stretched in an anomalous dispersion fiber. Thereafter, the light pulses broaden spectrally and temporally in an Erbium-doped fiber amplifier having normal dispersion. The laser beam leaving the fiber amplifier is collimated, and the chirped light pulses are compressed in a bulk silicon compressor to a pulse duration of about 100 fs. Thereafter, the light pulses are coupled into a HNLF. Light pulses tunable between 950 nm and 1400 nm are generated by exploiting the process of non-solitonic radiation during the soliton fission process in the HNLF. The frequency shift of the non-solitonic radiation to shorter wavelength is determined by the phase matching condition which depends on the parameters of the HNLF and on the peak power of the light pulses initially formed in the HNLF. Tuning is achieved by means of changing the peak power incident onto the HNLF. In the known system, the material passage of the silicon compression prisms is changed for this purpose. In this way, a chirp of the light pulses is generated which renders the peak power tunable in a targeted manner. By this approach in combination with a suitable HNLF, the non-solitonic radiation can be tuned between 1400 nm and 950 nm. However, a disadvantage of the known system is the necessity to include bulk elements and large free space sections containing the silicon prisms. Moreover, a motorized translation stage is required in order to change the prism separation for automated detuning. The arrangement of the silicon compression prisms causes instabilities due to temperature fluctuations, slows down the tuning speed and causes undesirable coupling losses.